A Battery-Input Three-Mode Buck–Boost Hybrid DC–DC Converter With 97.6% Peak Efficiency

This article presents a three-mode non-inverting buck–boost hybrid converter (3M-BBHC) suitable for mobile devices powered by lithium-ion (Li-ion) batteries. The proposed 3M-BBHC can work in buck, boost, or buck–boost mode, and it can switch the operation mode smoothly with a small ripple as the input voltage changes. Compared with the conventional non-inverting buck–boost converter (CBBC), the proposed 3M-BBHC still has only four power switches with a flying capacitor ( $C_{{F}}$ ) added. The number of switches conducting current in series with the inductor is reduced from 2 (in CBBC) to 1 (in 3M-BBHC) to decrease the conduction and switching losses. The inductor connects to the input terminal, which means the 3M-BBHC has a continuous input current and thus low electromagnetic interference (EMI). Besides, in buck mode, the inductor current is always smaller than the output current, which decreases the inductor dc resistance (DCR) conduction loss. The 3M-BBHC was fabricated in a standard 0.18- $\mu$ m CMOS process, using only 3.3-V devices to further reduce the losses. A 97.6% peak efficiency is measured by using a 2.2- $\mu$ H inductor with 110-m $\Omega$ DCR, a 10- $\mu$ F $C_{{F}}$ , a 10- $\mu$ F output capacitor ( $C_{{O}}$ ), and a 2-MHz switching frequency. Its input voltage ranges from 2.7 to 4.2 V, and it can deliver an output current of 100–800 mA at 3.3-V regulated output voltage.